The present invention relates to a two-dimensional absolute position sensor whose non-contact and magnetic features make its environment-resistance excellent and makes it possible to measure the position of a physical object by only installing a small magnetic slit thin plate on the object without making extensive alterations to it, and that can be applied as a position sensor of an end-effector of a clean/vacuum environment robot, and more specifically, a two-dimensional absolute position sensor that can facilitate correction of the position of an end-effector and perform the re-teaching of a robot.
Conventionally, in the field of semiconductor manufacturing devices, robots that can work in the clean/vacuum environment are generally used to transport silicon wafers and glass substrates for liquid crystal display panels. An end-effector is attached to the end of a robot arm as a movable objects that can hold or carry wafers and glass substrates and operate in a two-dimensional plane.
However, in the case where a certain problem occurs to the above-mentioned robots and it is necessary to re-teach their arms mounted with end-effectors, complicated re-teaching processes require considerable time and cause deterioration of throughput capacity in a subsequent process.
Also, aging loss of resilience of driving belt of robot arm gradually causes shift of end-effector.
To solve the above-mentioned problems and correct shift of end-effector, it is required to attach a small-sized, light-weighted two-dimensional absolute position sensor that does not need to make any extensive improvement to the structure of an end-effector in consideration of the thickness of the end-effector, which is only a few millimeters thick.
Particularly for robots operated in the clean/vacuum environment, generation of particles polluting the environment in which they are operated is not allowable and such robots might sometimes be used in a chemical solution. Position sensors, appropriate for robots operated in the clean/vacuum environment from the above-mentioned aspects, which have an excellent environment-resistance and can readily measure the two-dimensional absolute position of the end-effector in a non-contact manner, have not materialized and no official gazettes setting forth said art have been found.
The present invention is designed to solve the above-mentioned problems and aims at providing a two-dimensional absolute position sensor that can readily measure the two-dimensional absolute position of the end-effector in a non-contact manner if shift of the end-effectors of robots operated in the clean/vacuum environment is observed and that are environment-resistant as well as small-sized and light-weighted.
To solve the above-mentioned problems, the invention in Claim 1 relates to a two-dimensional absolute position sensor that measures the two-dimensional (in the X and Y directions) absolute position of a movable object that is attached to the end of a robot arm and moves in a plane. It comprises at least one magnetic slit thin plate having slits extending in the X and Y directions separately in the plane, where said movable object moves, magnetic sensor heads having magnetic sensors for position measurement in the X and Y directions opposed to the magnetic slit thin plate through a gap therebetween and bias magnets for applying magnetic fields to said magnetic sensor which is opposed to said magnetic slit thin plate through said magnetic sensor, and a signal processing circuit for outputting an absolute position signal generated from signals outputted from said magnetic sensors.
According to Claim 2 of the invention, a two-dimensional absolute position sensor of Claim 1, wherein said signal processing circuit comprises circuits determining an effective region, composed of the first comparator that compares levels of signals having different phases and obtained by one magnetic sensor for position measurement in one of the X and Y directions, amplitude detection circuits that detect the amplitude of signals obtained by the magnetic sensor for position measurement in the other direction, and the second comparator that compares the output of said amplitude detection circuits with a comparison voltage, said two-dimensional absolute position sensor specifies a measured region in one direction, by outputting effective signals of positions generated from the output of said first comparator and said second comparator, and similarly by specifying a measured region in the other direction, and thus a two-dimensional absolute position can be measured.
According to Claim 3 of the invention, a two-dimensional absolute position sensor of Claims 1 and 2, wherein said magnetic slit thin plate is either roughly cross-shaped or T-shaped.